PDCD1 and small cell lung carcinoma: The emergence of immunotherapy, particularly immune checkpoint inhibitors (ICIs) targeting programmed cell death protein 1 (PD-1), programmed cell death-ligand 1 (PD-L1), and cytotoxic T-lymphocyte-associated protein 4 (CTLA-4), has revolutionized the therapeutic landscape of ES-SCLC, improving the OS and progression-free survival (PFS) of patients (8).